Light Source Power Supply Anomalies

I’ve been meaning to write about power supplies for some time and a recent exchange reminded me of one of the reasons I was initially prompted to. Anyone who’s frequented this odd little website is aware of my feelings concerning used microscopes; in the words of a breakfast cereal mascot “they’re great!” One thing that is perhaps not so great, completeness. By this I of course refer to the tendency of second hand stands to be somewhat incomplete, particularly as regards light sources and power supplies.

Now the absence of a lamp housing and mount should, as a rule, be considered a deal breaker for a stand that requires one. Very rarely, one might find and recognize a needed lamp housing but the search is liable to be complicated by sellers who are uninformed and so list the item under difficult terms or worse by informed sellers who know the proper terms and therefore the rarity and value of the item. This isn’t about lamp housings though, this is about another component that if missing does not disqualify an otherwise complete or desirable stand from consideration; I write of course of the lamps power supply.

Another enthusiast contacted me with a question about a B&L transformer. As I looked through the manuals for a part number I noticed something interesting. Two versions of the manual for the Dynoptic & DynaZoom had two different sets of published voltages! One version of the manual described the five taps as having the first set of voltages, the other the second. Oddly enough each manual recommended the same GE-1634 lamp.

  1. 1v – 2.2v – 4.5v – 9v -21v
  2. 12v – 14v – 16.5v – 20v – 25v

Admittedly, that’s a 20v bulb, so it’s entirely possible that two version of the transformer were made. Somewhat more unusual is the lack of a specific part number listed in either manual for the transformer itself. B&L at one time or another assigned part numbers to everything from screws to shims, so I’m a little concerned that I only failed in my search because I didn’t read as carefully as I might have. I took a multimeter to each of the corresponding transformers in my collection and both proved to me of the higher voltage varieties. It’s not at all uncommon for a microscope illuminator to provide higher voltage than that for which the bulb is rated. In older textbooks and even on some modern transformers the final tap, or range on continuously variable transformers, is marked as “OV” for over voltage generally called over run. The fact that the second set is so much higher than the first would tend to disqualify the first transformer for photomicrographic work. I’d go so far as to say the binocular heads should not used with the first transformer if one intends to use a daylight filter, and the second shouldn’t be used for visual work without one, or at least a set of neutral density filters.

What I’d like to point out, is not that the published voltages of a transformer may not line up with a transformer that “looks like” the one in hand, or that is available for purchase. Rather, that the important thing is the supply provided by the transformer and its suitability not only for the bulb employed but also the intended use. It’s a simple thing really, and something that might be forgiven for someone who’s only had to deal with common lightbulbs of the sort had at the average home store or hardware. Where then should the enterprising microscopist begin in outfitting a microscopes illumination system? With the correct bulb. The correct bulb will be mechanically compatible with the bulb holder and lamp house as well as of the rated wattage.

I write of wattage because at the beginning the most important and most frequently overlooked characteristic of a bulb is the heat which it will put out. Over high wattages will present a fire hazard, apart from the potential damage to a stand one might also damage the eyes, so do consider the wattage when choosing a replacement bulb. If at all possible always use the bulb recommended by the manufacturer, or a mechanically compatible bulb of lower wattage.

And this weekend, the part I’ve been meaning to write! -K

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